1. Field of the Invention
This invention relates to improved apparatus and methods for levelling metal plate, particularly heavy metal plate which exerts high separating forces tending to distort the work rolls and resulting in non-uniform levelled plate dimensions. The invention is directed especially to improved means and methods for automatically compensating for work roll distortion under such heavy loads and thereby providing uniformly dimensioned product.
2. Description of Related Art
U. S. Pat. No. 3,596,489 discloses an apparatus for processing sheet or strip material between a pair of work rolls and including a flexible beam supported at its ends in the apparatus housing and a further beam relatively stiff compared to the flexible beam. Back-up rolls are mounted on the underside of the flexible beam and engage a number of upper work rolls. As the work rolls deflect under load, the flexible beam is flexed by a number of hydraulically or pneumatically driven piston/cylinder assemblies to apply compensating forces along the length of the upper work roll in opposition to forces acting on the roll due to material in the roll gap. The fixed ends of the flexible beam limit the size and distribution of compensating forces applicable through the flexible beam and require the use of movable piston/cylinder assemblies which are slidably mounted across the length of the work rolls. Moreover, the invention of this patent requires manual control of application of the compensating forces in response to changes in roll distortion due to the roll separation forces.
U.S. Pat. No. 4,730,472 discloses a leveller wherein upper back-up rolls are mounted on an intermediate support frame of limited flexure and which can be flexed, by means of a plurality of hydraulic piston/cylinder assemblies fixed in a top main frame of the apparatus, in order to contour the levelling action. Each cylinder is controlled by a servo valve which can be adjusted by the operator to work sheet material across its width, depending on sheet flatness. Variations in sheet thickness result in variation in pressures against the working roll nearest the defect, which pressures are transferred to back-up rolls and thence to the flexible intermediate beam which then tends to flex and compensate for such pressure excursions. Such flexure causes movement of the piston and such movement is sensed by a position transducer to generate a signal to a summing amplifier which compares the input signal to a reference position signal. Amplifier output then actuates the servo valve and a pump motor to send hydraulic fluid to the affected cylinder or to vent cylinder pressure, thus restoring the piston to an initial position to counter the loading variation on the work roll caused by the sheet material. Thus, automatic control of the piston/cylinder assemblies is actuated only by variations in thickness of material being processed. There is no provision for continuous monitoring and correction of deflection of the top or bottom beams respectively carrying the top and bottom roll assemblies.